Whiplash Symptoms - Low Back Pain

Over the last 10 years, hundreds of studies have been done on the problem of whiplash, and most of those studies have focused on the most common symptom of the diagnosis: neck pain. This concentration of research has resulted in a clear understanding of how a rear-end collision can result in injury.

Shear forces occur when one part of the
spine moves in one direction while another
part of the spine moves in a different direction.

Shear forces can cause tearing or stretching
of the soft tissues that hold the spine together.

The primary reason why rear-end collisions cause injury is that the human spine is designed to withstand vertical forces, while a rear-end collision is a horizontal force. The vertical forces are known as “axial” forces. The horizontal forces, known as “shear” forces, cause unnatural movements of the cervical spine and can result in damage to the ligaments of the neck.

A new study has now shown that a similar injury mechanism occurs in the lumbar spine as well. Inspired by the research on the cervical spine, the authors of this study applied the same methodology to the low back.

They placed a cadaver in a standard automotive seat and placed acceleration-measuring devices in the vertebral bodies of T1, L1, L3, and L5. The seat was placed on a platform that was subjected to rear accelerations of 5g and 8g, or speeds of approximately 8 and 12 mph, respectively. The researchers collected acceleration data at a rate of 10,000 samples per second. Radiographs were taken of the spine before and after the tests.
The study found that different parts of the lumbar spine experience different strains during a rear-end impact:

“The anterior shear strains had mostly a biphasic response. Spinal strains started at about 30 msec after impact and peaked at the T12 vertebra at approximately 120 and 370 msec, whereas in the L4 vertebra, it peaked at 200 and 380 msec. The anterior strain patterns of the L4 and T12 vertebrae were in diametrically opposite directions.”

The direction and strength of the forces suggests that the car seat rapidly accelerates into the occupant’s spine, causing the thoracic and lumbar curves to straighten.

The authors of the study carefully examined the forces involved in the spine during the test impacts. They found that the car seat exerted about 1500 Newtons (approximately 337 pounds) of force, in a fraction of a second. The authors relate this to how the lumbar spine can be injured in rear end collisions:

“In the current study, no bony injuries were observed in the lumbar spine, either by visual inspection or by radiographic studies. In the absence of clear bony pathology after rear-impact collision, we propose that irritation of or injury sustained by the richly innervated spinal soft tissues (i.e., muscles, ligaments, capsules) plays an important role in the pathogenesis of lumbar pain after whiplash injury. This proposition is supported by work of others who performed lumbar spinal segment shear tests and showed that soft-tissue injuries occurred with a shear load as low as 1200 N.”

The 1500 Newtons of force was reached in the 5g test, which was equivalent to an 8 mph collision. So, according to this preliminary study, the car seat back exerts enough force during such a collision to injure the connective tissue of the lumbar spine.

Fast A, Sosner J, Begeman P, et al. Lumbar spinal strains associated with whiplash injury. American Journal of Physical Medicine and Rehabilitation 2002;81:645-650.

Whiplash, Referred Pain and the Central Nervous System

The most frequent symptoms after whiplash injury are headache and neck pain, which are understandable, since the neck is directly injured during a rear-end collision. Many auto injury patients, however, experience a much wider range of symptoms. Arm pain, shoulder pain, back pain, TMJ pain, and dizziness are also very common symptoms, and these are difficult to ascribe to direct trauma. A new study shows us that these other symptoms are actually related to the initial neck trauma, through the process of referred pain.

Referred pain is pain that is perceived in one area, but that originates in another. Researchers believe that referred pain occurs when pain signals from injured tissue activate adjacent nerves in the spinal cord or brain. These adjacent nerves then cause the brain to perceive pain in the area of the body innervated with those nerves.

Referred pain can be induced, even in pain-free people. In a new study from Sweden, researchers set out to determine whether whiplash patients had a different referred pain response to stimulus than non-whiplash subjects.

The authors started with 12 patients and 12 pain-free control subjects. Referred pain was created by electrical stimulation of the shoulder and the upper arm. The electrical stimulation level was set by the test subjects, and was adjusted to create five progressive levels of pain – innocuous, pain threshold, 2 out of 10, 4 out of 10, 6 out of 10 (on a scale of 1 to 10).

The results showed a dramatic difference between patients and controls:

1. Pain-free subjects required almost three times more stimulation to reach the designated pain levels than did the whiplash subjects.
2. While the controls reported limited areas of referred pain, the whiplash patients reported a much wider area of referred pain.
3. Whiplash patients showed a unique type of referred pain. In healthy individuals, induced referred pain was always distal to the stimulation (or further from the center of the body), but in the whiplash patients, half of the patients had referred pain that was proximal to the stimulation.

These findings are important in understanding the nature of whiplash injuries. As previous studies have shown, some whiplash patients demonstrate “central hypersensitivity,” a phenomenon where the central nervous system becomes over-stimulated from the injury to the spine.

According to the literature, a certain percentage of patients are susceptible to chronic pain after an auto injury. In these patients, central nervous system changes may develop in reaction to pain, which can, in turn, increase the patient’s sensitivity to pain. It is critical to identify these patients early on after injury, in order to break this cycle. Sensory tests, such as pressure pain threshold testing, are an important diagnostic tool, since they can help us identify those patients with a posttraumatic stress reaction.

Kosek E, Januszewska A. Mechanisms of pain referral in patients with whiplash associated disorder. European Journal of Pain 2008;12:650-660.

Multidisciplinary Treatment For Chronic Whiplash

The purpose of this study was to assess the effectiveness of a multimodal treatment program for patients with chronic symptoms after whiplash. 26 patients (13 male, 13 female) participated. All had experienced whiplash at least six months before the study and had experienced symptoms for an average of 20.8 months. All were partially or completely unable to work and had been absent from work for an average of 15.7 months.

A multidisciplinary team assessed all patients before treatment began. An orthopedic surgeon or neurologist conducted a full physical exam and assessed radiographs including extension-flexion films of the cervical spine. A physical therapist looked at cardiorespiratory fitness. Psychological assessment using MMPI-2 was done by a clinical psychologist. Neuropsychological screening was also done. An occupational therapist assessed the physical and mental demands of each patient's work. These assessments were used as baseline data to be compared with outcome data. Results of these assessments were shared with patients (and their partners) before the treatment program began.

Patients participated in a daily 4-week outpatient multimodal treatment aimed at restoring normal daily function. The patients were instructed to not use analgesics. It was explained that the purpose of the study was not to reduce pain, per se, but to increase regular functioning- including return to work. The program included physical training meant to end inappropriate pain behavior, restore muscle endurance and strength and to improve aerobic fitness. Group sessions were employed to discuss patient's deeply held beliefs on symptoms and disability.

Program outcome was measured using both self-report & objective criteria. Self-report measures included neck pain, headache, disability, fatigue, "vague" somatic symptoms, psychological distress, depression, and problems with concentration and memory. Objective measures looked at features of daily functioning such as return to work, drug usage, and medical consumption.

A six-month follow up assessment documented the program outcome. Statistically significant improvements on self-report measures were found. For somatic symptoms, 73% of patients fell within normal range. 96% rated within normal limits for psychological distress. 46% of patients were within normal health distribution for pain intensity (reportedly, nearly pain free). This improvement in pain levels occurred despite the fact that the treatment goal did not include pain reduction, and many of the activities required in the program could have increased pain. Follow up assessment of objective criteria showed a complete return to work for 65% of patients and at least partial return to work for 92% of patients. 81% of patients did not seek medical care during the follow up period. Only 58% of the patients reported no use of analgesics.

While improvement was noticeable in a segment of the test subjects, there were still a number of patients with pain symptoms. The authors address this issue:

"As has been established for chronic low back pain, cognitive behavioral treatment appears to be a promising treatment for patients with chronic symptoms after a whiplash injury. However, considering that more than 50% of patients did not show a clinically significant change and 35% of patients did not achieve a complete return to work, it is clear that there is still a great deal of work to be done. The question is, why did some patients not improve?"

The authors suggest that patient beliefs are responsible for chronic whiplash symptoms, and they refer to the severely flawed Quebec Task Force and the Lithuanian studies as evidence that there are no physical reasons for chronic pain. The study completely ignores the vast body of literature on whiplash biomechanics that isolate the cervical facet joints as a cause of pain after whiplash injuries.

Vendrig A, van Akkerveeken P, McWhorter K. Results of a multimodal treatment program for patients with chronic symptoms after a whiplash injury of the neck. Spine 2000;25(2):238-244.